Effects of the selective disruption of within- and across-channel cues to comodulation masking release

In many experiments on comodulation masking release (CMR), both across- and within-channel cues may be available. This makes it difficult to determine the mechanisms underlying CMR. The present study compared CMR in a flanking-band (FB) paradigm for a situation in which only across-channel cues were likely to be available [FBs placed distally from the on-frequency band (OFB)] and a situation where both across- and within-channel cues might have been available (proximally spaced FBs, for which larger CMRs have previously been observed). The use of across-channel cues was selectively disrupted using a manipulation of auditory grouping factors, following Dau et al. [J. Acoust. Soc. Am. 125, 2182-2188(2009)] and the use of within-channel cues was selectively disrupted using a manipulation called "OFB reversal," following Goldman et al. [J. Acoust. Soc. Am. 129, 3181-3193 (2011)]. The auditory grouping manipulation eliminated CMR for the distal-FB configuration and reduced CMR for the proximal-FB configuration. This may indicate that across-channel cues are available for proximal FB placement. CMR for the proximal-FB configuration persisted when both manipulations were used together, which suggests that OFB reversal does not entirely eliminate within-channel cues.     

Within-channel cues to comodulation masking release for single and symmetrically placed pairs of flanking bands

Comodulation masking release (CMR) as measured in a flanking-band (FB) paradigm is often larger when the FBs are close to the signal frequency, f(s), than when they are remote from f(s), an effect which may be partly due to the use of within-channel cues. Schooneveldt and Moore [J. Acoust. Soc. Am. 85, 262-272 (1989)] reported that, for f(s) = 1000 Hz, this effect was larger when a single FB was used than when there were two FBs symmetrically placed about f(s), and proposed that there are within-channel cues that are available for a single FB, but not for a symmetrically placed pair of FBs. The present study replicated and extended their study. Although CMR was larger for two symmetrically placed FBs than for a single FB, the effect of FB proximity to f(s) did not differ for the two cases. The results do not support the idea that there are additional within-channel cues that are available for a single FB. Changes in the regularity of temporal fine structure and changes in the prevalence of low-amplitude envelope portions are both plausible within-channel cues.     

Disrupting within-channel cues to comodulation masking release

Comodulation masking release (CMR), assessed using a flanking-band (FB) paradigm, may reflect the contribution of both across- and within-channel cues when FBs are proximal to the signal frequency. This study examined the effect of disrupting within-channel cues based upon envelope beats at the output of an auditory filter centered at the signal frequency, using a method described by Richards [(1988) Hear. Res. 35, 47-58], here called "on-frequency band (OFB) reversal." This removed regular beats for a pair of proximal FBs centered symmetrically about the OFB on a linear frequency scale (but not for a single FB that had the same center frequency as either of the constituent FBs in a pair) while maintaining the comodulation of individual noise bands that provides the basis for across-channel processes. OFB reversal consistently reduced CMR for proximal FB pairs--but not for a single FB or distal FB pair or when the FBs were presented in the opposite ear to the signal plus OFB--across a range of signal frequencies and for continuous and gated noise presentation. Simulations indicated that OFB reversal reduces the availability of within-channel cues based upon temporal fine structure and changes in envelope statistics.     

Influence of place synchrony on detection of a sinusoid

A series of experiments was performed to study the ability of the ear to code the temporal envelope of a waveform as demonstrated by comodulation masking release (CMR). The stimulus for all experiments was composed of a tone-burst signal, a 100-Hz-wide masker band centered at the signal frequency, and a second 100-Hz-wide noise band of variable frequency, the cue band. The cue band had a temporal envelope which was either correlated with or independent of that of the masker. The signal was a 100-Hz tone burst for most experiments. For the monotic stimulus, the correlated cue band results in lowered signal detection thresholds over a range extending from around 2/3 oct below the signal frequency to 1/3 oct above that frequency. When measured dichotically, with the signal and masker band in one ear and the cue band in the opposite ear, that effective range is expanded but the detection threshold shifts are a bit smaller. The greatest CMR is observed when the stimulus is presented diotically. With regard to effects of level and frequency, our data show CMR increasing with increasing stimulus level for a cue band lower in frequency than the signal, but show little effect of level for a cue band higher in frequency. Similarly, CMR increases with increasing stimulus frequency when the cue band is lower in frequency, but shows little effect of frequency for a cue band higher in frequency.     

Effects of stimulus frequency on two-tone suppression: a comparison of physiological and psychophysical results

The effects of stimulus frequency on two-tone suppression were investigated in single auditory-nerve fibers of anesthetized cats and compared with human psychophysical data. In the physiological experiment, both average discharge rate and phase-locked activity were measured in response to one- and two-tone stimuli. The first component f1 produced an increase in rate above spontaneous activity when presented alone. The second tone f2 was always well below the fiber's characteristic frequency and was held at a fixed sound pressure level appropriate to produce two-tone suppression. Responses were plotted as a function of stimulus level of the first tone both alone and in the presence of f2. For different values of f1 with f2 fixed, suppression was maximum with f1 near fiber CF. In the psychophysical experiment, similar stimulus parameters of f1 and f2 were used as the masker in a forward-masker paradigm. In this experiment the addition of the second masker tone at frequency f2 could produce less masking of the signal. When f1 was varied with f2 fixed, the relative decrease in masking, analogous to suppression, was greatest when f1 was equal to the signal frequency.     

Growth of suppression in humans based on distortion-product otoacoustic emission measurements

Distortion-product otoacoustic emissions (DPOAEs) were used to describe suppression growth in normal-hearing humans. Data were collected at eight f(2) frequencies ranging from 0.5 to 8 kHz for L(2) levels ranging from 10 to 60 dB sensation level. For each f(2) and L(2) combination, suppression was measured for nine or eleven suppressor frequencies (f(3)) whose levels varied from -20 to 85 dB sound pressure level (SPL). Suppression grew nearly linearly when f(3) ≈ f(2), grew more rapidly for f(3)?< f(2), and grew more slowly for f(3)?> f(2). These results are consistent with physiological and mechanical data from lower animals, as well as previous DPOAE data from humans, although no previous DPOAE study has described suppression growth for as wide a range of frequencies and levels. These trends were evident for all f(2) and L(2) combinations; however, some exceptions were noted. Specifically, suppression growth rate was less steep as a function of f(3) for f(2) frequencies ≤ 1 kHz. Thus, despite the qualitative similarities across frequency, there were quantitative differences related to f(2), suggesting that there may be subtle differences in suppression for frequencies above 1 kHz compared to frequencies below 1 kHz.     

Comodulation masking release: evidence for multiple cues

Signal detection was determined in conditions where the masker was a 10-Hz-wide noise band centered on the signal, and in conditions where either a comodulated or noncomodulated noise band (centered at 0.8 times the signal frequency) was also present. Signal frequencies of 500 or 2000 Hz were investigated. In one condition of the first experiment, the signal was exactly the same 10-Hz-wide noise band as the masker, added to the masker in phase. This condition was designed to limit the availability of cues based upon dip listening, suppression, beating, or across-frequency differences in noise envelope correlation, but to afford a cue based upon across-frequency envelope amplitude difference. The narrow-band noise signal resulted in approximately the same magnitude of comodulated masking release (CMR) as was found for a pure-tone signal. This result suggested that one important cue for CMR is an across-frequency difference in envelope amplitude. Stimulus conditions in the second experiment were intended to disrupt cues of across-frequency envelope amplitude difference, but to afford cues based upon across-frequency differences in noise envelope correlation. In this experiment, cues based upon envelope amplitude were impoverished by randomly varying the level of the flanking band from interval to interval, and by adjusting the level in the on-signal band to be the same in the nonsignal intervals as the level of noise plus signal in the signal interval. Again, substantial CMRs occurred, suggesting that another cue for CMR may be envelope pattern or correlation. The results of these experiments indicated that CMR is probably based upon more than one stimulus variable.     

Non-contrast enhanced diagnosis of acute myocarditis based on the 17-segment heart model using 2D-feature tracking magnetic resonance imaging

PurposeThe aim of this study was to investigate the diagnostic value of myocardial deformation analysis based on the 17-segment heart model using non-contrast enhanced (CE) 2D tissue feature tracking (2D-FT) technique.Material and methodsSeventy patients with suspected myocarditis underwent a cardiovascular magnetic resonance (CMR) examination at 1.5 Tesla. A contrast-agent-free part of this CMR protocol was additionally performed in forty healthy volunteers (HV). Besides standard CMR data sets, 2D-FT derived segmental and global longitudinal, radial, and circumferential deformation parameters were analyzed. The 2D-FT results were compared to the combined findings from CMR imaging and endomyocardial biopsy (EMB).ResultsPatients were assigned to three groups depending on their ejection fraction (EF) (<40%, 40–55%, ≥55%). Compared to HV, impaired EF (<55%) was significantly correlated to reduced segmental and global strain and strain rate values. The circumferential deformation analysis was more sensitive to myocardial changes than longitudinal and radial analysis. The segmental strain/strain rate had an accuracy of 84.3%/70.0% for the diagnosis of an acute myocarditis, stated by EMB and CMR in 42 of 70 patients. In patients with preserved EF, acute myocarditis could be ruled out using only segmental strain analysis with a negative predictive value of 87.5%.ConclusionIn patients with suspected myocarditis, the deformation analysis based on the 17-segment heart model provides valuable information about functional myocardial inhomogeneity. This quantitative approach could be used in addition to the clinical standard CMR protocol and represents a promising tool in the framework of a prospective automatized multiparametric CMR imaging analysis.     

Comodulation masking release (CMR): effects of signal frequency, flanking-band frequency, masker bandwidth, flanking-band level, and monotic versus dichotic presentation of the flanking band

In experiment I, thresholds for 400-ms sinusoidal signals were measured in the presence of a continuous 25-Hz-wide noise centered at signal frequencies (fs) ranging from 250 to 8000 Hz in 1-oct steps. The masker was presented either alone or together with a second continuous 25-Hz-wide band of noise (the flanking band) whose envelope was either correlated with that of the on-frequency band or was uncorrelated; its center frequency ranged from 0.5 fs to 1.5 fs. The flanking band was presented either in the same ear (monotic condition) as the signal plus masker or in the opposite ear (dichotic condition). The on-frequency band and the flanking band each had an overall level of 67 dB SPL. The comodulation masking release, CMR (U-C), is defined as the difference between the thresholds for the uncorrelated and correlated conditions. The CMR (U-C) showed two components: a broadly tuned component, occurring at all signal frequencies and all flanking-band frequencies, and occurring for both monotic and dichotic conditions; and a component restricted to the monotic condition and to flanking-band frequencies close to fs. This sharply tuned component was small for low signal frequencies, increased markedly at 2000 and 4000 Hz, and decreased at 8000 Hz. Experiment II showed that the sharply tuned component of the CMR (U-C) was slightly reduced in magnitude when the level of the flanking band was 10 dB above that of the on-frequency band and was markedly reduced when the level was 10 dB below, whereas the broadly tuned component and the dichotic CMR (U-C) were only slightly affected. Experiment III showed that the sharply tuned component of the CMR (U-C) was markedly reduced when the bandwidths of the on-frequency and flanking bands were increased to 100 Hz, while the broadly tuned component and the dichotic CMR (U-C) decreased only slightly. The argument here is that the sharply tuned component of the monotic CMR (U-C) results from beating between the "carrier" frequencies of the two masker bands. This introduces periodic zeros in the masker envelope, which facilitate signal detection. The broadly tuned component, which is probably a "true" CMR, was only about 3 dB.     

Within-channel cues in comodulation masking release (CMR): experiments and model predictions using a modulation-filterbank model

Experiments and model calculations were performed to study the influence of within-channel cues versus across-channel cues in comodulation masking release (CMR). A class of CMR experiments is considered that are characterized by a single (unmodulated or modulated) bandpass noise masker with variable bandwidth centered at the signal frequency. A modulation-filterbank model suggested by Dau et al. [J. Acoust. Soc. Am. 102, 2892-2905 (1997)] was employed to quantitatively predict the experimental data. Effects of varying masker bandwidth, center frequency, modulator bandwidth, modulator type, and signal duration on CMR were examined. In addition, the effect of band limiting the noise before or after modulation was shown to influence the CMR in the same way as a systematic variation of the modulation depth. It is demonstrated that a single-channel analysis, which analyzes only the information from one peripheral channel, quantitatively accounts for the CMR in most cases, indicating that an across-channel process is generally not necessary for simulating results from this class of CMR experiments. True across-channel processes may be found in another class of CMR experiments.     

Rate coding model for discrimination of simple tones in the presence of noise

The predictions of a rate coding model for frequency and amplitude jnd's in the presence of noise are presented for a 1-kHz, 100-ms tone. The model for the neural response incorporates physiological data on dynamic range distribution and rate suppression. A central processor is assumed to estimate the tone frequency, or amplitude, from the tone-evoked rate increment profile. This central processor acts like an ideal detector with respect to the neural noise. The effects of the neural noise as well as the signal variability on the discrimination performance level are evaluated, and the signal variability is found to be significant. The combined effect of threshold distribution, rate suppression, and signal variability make the jnd's practically invariant with noise level, in accordance with published psychophysical data. The values of the frequency jnd at high signal-to-noise ratio, however, are borderline in their consistency with the data. A more obvious discrepancy exists between the model and the psychophysical data regarding the ratio of frequency to amplitude Weber fractions, which can be resolved only by modifying the model auditory filters to be five times sharper than those measured in cats.     

Comodulation masking release: effects of training and experimental design on use of within- and across-channel cues

The effects of training and experimental design on comodulation masking release (CMR) were assessed. The study of Dau et al. [(2009), J. Acoust. Soc. Am. 125, 2182-2188], which used auditory-grouping manipulations to distinguish the use of within- and across-channel cues to CMR, was replicated in Experiment One but using naive subjects and an experimental design that minimized familiarization with the cues. Subjects made effective use of within- but not across-channel cues. Experiment Two examined training effects over more testing sessions, across four experimental designs (to minimize or maximize repeated exposure to the cues) and using an auditory grouping manipulation ("postcursors") to distinguish the use of within- and across-channel cues. Naive subjects were tested with either two or four flanking bands (FBs), to determine if training effects varied with the amount of FB information. Within-channel cues could be used from the outset, but effective use of across-channel cues required training when they were less salient. Increased repeated exposure enhanced the effects of training. Experiment Three tested naive subjects using two FBs, but with noise presented continuously and a different auditory grouping manipulation, after Grose et al. [(2009), J. Acoust. Soc. Am. 125, 282-293]. CMR was large from the outset.     

Psychophysical suppression measured with bandlimited noise extended below and/or above the signal: effects of age and hearing loss

The objectives of this study were to measure suppression with bandlimited noise extended below and above the signal, at lower and higher signal frequencies, between younger and older subjects, and between subjects with normal hearing and cochlear hearing loss. Psychophysical suppression was assessed by measuring forward-masked thresholds at 0.8 and 2.0 kHz in bandlimited maskers as a function of masker bandwidth. Bandpass-masker bandwidth was increased by introducing noise components below and above the signal frequency while keeping the noise centered on the signal frequency, and also by adding noise below the signal only, and above the signal only. Subjects were younger and older adults with normal hearing and older adults with cochlear hearing loss. For all subjects, suppression was larger when noise was added below the signal than when noise was added above the signal, consistent with some physiological evidence of stronger suppression below a fiber's characteristic frequency than above. For subjects with normal hearing, suppression was greater at higher than at lower frequencies. For older subjects with hearing loss, suppression was reduced to a greater extent above the signal than below and where thresholds were elevated. Suppression for older subjects with normal hearing was poorer than would be predicted from their absolute thresholds, suggesting that age may have contributed to reduced suppression or that suppression was sensitive to changes in cochlear function that did not result in significant threshold elevation.     

Modeling cochlear dynamics: interrelation between cochlea mechanics and psychoacoustics

A model of the cochlea was used to bridge the gap between model approaches commonly used to investigate phenomena related to otoacoustic emissions and more filter-based model approaches often used in psychoacoustics. In the present study, a nonlinear and active one-dimensional transmission line model was developed that accounts for several aspects of physiological data with a single fixed parameter set. The model shows plausible excitation patterns and an input-output function similar to the linear-compressive-linear function as hypothesized in psychoacoustics. The model shows realistic results in a two-tone suppression paradigm and a plausible growth function of the 2f(1)-f(2) component of distortion product otoacoustic emissions. Finestructure was found in simulated stimulus-frequency otoacoustic emissions (SFOAE) with realistic levels and rapid phase rotation. A plausible "threshold in quiet" including finestructure and spontaneous otoacoustic emissions (SOAE) could be simulated. It is further shown that psychoacoustical data of modulation detection near threshold can be explained by the mechanical dynamics of the modeled healthy cochlea. It is discussed that such a model can be used to investigate the representation of acoustic signals in healthy and impaired cochleae at this early stage of the auditory pathway for both, physiological as well as psychoacoustical paradigms.     

Wavelet based noise suppression technique and its application to ultrasonic flaw detection

The noise suppression techniques with wavelet transform (WT) are widely used in non-destructive testing and evaluation (NDT&E), especially in ultrasonics. Complete reconstruction theory with hard or soft thresholds, reconstruction technique based on the singularities of noise and signal, matched filter with an impulse response, and optimal frequency-to-bandwidth ratio of wavelet technique have all been used to analyze ultrasonic signals for noise suppression. But a more simple and effective technique has been pursued for decades. This paper develops a new technique using WT for the right purpose. In this work, WT is treated as a band-pass filter whose central frequency and frequency bandwidth (CF&FB) are determined by the spectra distribution of an ultrasonic signal captured from real testing situation. For the purpose of matching their CF&FB well, a technique for evaluating the optimal scale of a daughter wavelet is carried out too. By acting this daughter wavelet as a band-pass filter, we can obtain excellent de-noising results, even when the signal to noise ratio (SNR) is below -18 dB. The performance of the technique has been done by ultrasonic signals with computer generated white noises. Finally, the experimental verification is performed on a pipeline specimen with man-made small flaws with good results obtained. The results show that the technique is more suitable for processing heavy noised ultrasonic signals, and it can also be used in automatic flaw detection.     

Monaural envelope correlation perception, revisited: effects of bandwidth, frequency separation, duration, and relative level of the noise bands

This article presents the results of two experiments investigating performance on a monaural envelope correlation discrimination task. Subjects were asked to discriminate pairs of noise bands that had identical envelopes (referred to as correlated stimuli) from pairs of noise bands that had envelopes which were independent (uncorrelated stimuli). In the first experiment, a number of stimulus parameters were varied: the center frequency of the lower frequency noise band in a pair, f1; the frequency separation between component noise bands; the duration of the stimuli; and the bandwidth of the component noise bands. For a long stimulus duration (500 ms) and a relatively wide bandwidth (100 Hz), subjects could easily discriminate correlated from uncorrelated stimuli for a wide range of frequency separations between the component noise bands. This was true both when f1 was 350 Hz, and when f1 was 2500 Hz. In each case, narrowing the bandwidth to 25 Hz, or shortening the duration to 100 ms, or both, made the task more difficult, but not impossible. In the second experiment, the level of the higher frequency noise band in a pair was varied. Performance did not decrease monotonically as the level of this band was decreased below the level of the other band, and only showed marked impairment when the level of the higher frequency band was at least 60 dB below that of the lower frequency band. The pattern of results in these two experiments is different from that which is obtained when the same stimulus parameters are varied in experiments investigating comodulation masking release (CMR). This suggests that the mechanisms underlying CMR and those underlying the discrimination of envelope correlation are not identical.     

Wave guiding properties and sensitivity of D-shaped optical fiber microwire devices

D-shaped optical fiber microwire (OFM) devices are investigated theoretically. They can be obtained by wrapping OFMs on removable rods or laying the OFMs on disposable substrates. Optical wave guiding properties of these devices are discussed with numerical simulations. Dispersion properties of OFMs with different radii are studied as well. A grating-based D-shaped OFM is proposed for sensing applications. The corresponding sensitivity could reach 1100 nm/RIU (refractive index unit) due to its large outside evanescent field.     

The effects of bandwidth on the detectability of narrow- and wideband signals

The effects of masker bandwidth on the detection of narrow- and wideband signals have been investigated. For both kinds of signals, plots of threshold as a function of masker bandwidth yielded by both narrow- and wideband signals are reasonably described with two intersecting lines. Threshold initially increase with masker bandwidth and then become independent of further increases. The rate of increase depends on the signal spectrum. The bandwidth at which the lines intersect varies with signal bandwidth and also mode of masker presentation (i.e., whether the masker is gated with the signal or is present continuously). Internal filtering is most accurate when the masker is present continuously. A model is proposed in which a listener's decisions about the presence of narrow-band signals are based upon estimates of stimulus energy within a critical band. These estimates are degraded by bandwidth-dependent processing errors. When the signal to be detected spans several critical bands (i.e., is wideband), the model forms a test statistic by summing the outputs of the relevant critical bands. The model permits the contribution of each band to the sum to vary with masker bandwidth because it incorporates a form of lateral suppression. Thresholds of narrow-band signals in gated maskers and wideband signals in gated and continuous maskers are predicted by the model. However, the model fails to account for the detectability of narrow-band signals in continuous maskers.     

Modeling comodulation masking release using an equalization-cancellation mechanism

This study presents an auditory processing model that accounts for the perceptual phenomenon of comodulation masking release (CMR). The model includes an equalization-cancellation (EC) stage for the processing of activity across the audio-frequency axis. The EC process across frequency takes place at the output of a modulation filterbank assumed for each audio-frequency channel. The model was evaluated in three experimental conditions: (i) CMR with four widely spaced flanking bands in order to study pure across-channel processing, (ii) CMR with one flanking band varying in frequency in order to study the transition between conditions dominated by within-channel processing and those dominated by across-channel processing, and (iii) CMR obtained in the "classical" band-widening paradigm in order to study the role of across-channel processing in a condition which always includes within-channel processing. The simulations support the hypothesis that within-channel contributions to CMR can be as large as 15 dB. The across-channel process is robust but small (about 2-4 dB) and only observable at small masker bandwidths. Overall, the proposed model might provide an interesting framework for the analysis of fluctuating sounds in the auditory system.     

一种采用互补结构的宽阻带共模缺陷地滤波器

为了抑制高速差分信号传输中的共模噪声, 提出了一种基于低成本FR4材料制作的互补型缺陷地结构(defected ground structure, DGS)共模阻带滤波器. 滤波器两边采用对称性酒杯形DGS结构, 中间采用对称伞形DGS结构. 由于这两种DGS 结构互补, 整个滤波器结构紧凑, 可以实现小面积设计目的; 另外, 由于三个DGS结构相邻较近, 相互之间存在互感, 可以通过改变相互之间的距离来调节相互之间的互感, 从而实现宽阻带滤波的目的. 仿真和测试结果表明, 该DGS滤波器的差模信号损耗小, 在抑制共模噪声20 dB条件下其阻带范围为4.8–11.4 GHz, 而且面积仅为10 mm×10 mm. 与周期性DGS结构相比, 本方法在相同共模噪声抑制深度下, 具有占用面积不到30%、阻带宽度增加约50%等优点.